1. Field of the Invention
The present invention relates to a communication system and apparatus for performing data communication through a digital communication network, e.g., an ISDN having a plurality of data channels and a control channel.
2. Prior Art
As a widely used terminal apparatus connected to a telephone network, a telephone terminal apparatus mainly using speech data is known. However, along with recent development of the communication techniques, a facsimile apparatus as a terminal which can exchange both image data and character data, and a personal computer comprising a modem are widely used.
Of these terminals, a terminal apparatus which can exchange both speech data and non-speech data like a facsimile apparatus with a telephone set is also available.
When a terminal apparatus of this type connected to the telephone network calls another terminal apparatus, the telephone network selects a designated called (call incoming side) terminal apparatus, and sends a call (ringing) signal to the called terminal apparatus. Upon reception of the call signal, the called apparatus detects that it is being called, and executes corresponding call incoming processing.
When a connecting request (call request) is made to a terminal apparatus of this type connected to the telephone network, the telephone network sends a call (ringing) signal to the requested terminal apparatus.
However, the called terminal apparatus receives only the call (ringing) signal, and can only determine that it is being called. As a result, it cannot discriminate where and what type of terminal apparatus transmitted the calling signal.
More specifically, at this time, the called terminal apparatus and a plurality of receiving parties who utilize the called terminal apparatus cannot discriminate who should receive reception data and the like.
For this reason, someone must answer the phone to identify a receiving party who is to receive data, resulting in time-consuming operation.
For example, when an operator makes a call from a telephone to another facsimile apparatus with a telephone for the purpose of verbal communication (speech communication), if the called facsimile apparatus with the telephone is set in an automatic reception mode, communication by means of the telephone cannot be performed, and digital data communication is immediately started.
One subscriber's line and a plurality of terminals can be connected to an ISDN (integrated service digital network). The present applicant filed, as Japanese Patent Application No. 62-316003, an application of an invention to change a ringer for calling an operator based on a subaddress (a command for selecting one of the plurality of terminals) sent from a terminal on the other end of a line. An operator can recognize the designated terminal through the signal sent by the terminal on the other end of the line. However, when one terminal is used by a plurality of operators, a designated terminal can be recognized but it cannot be recognized to whom of the plurality of operators the incoming call is made.